Isaac
Asimov was the most prolific science fiction author of all time. In fifty years
he averaged a new magazine article, short story, or book every two weeks, and
most of that on a manual typewriter. Asimov thought that The Last Question,
first copyrighted in 1956, was his best short story ever. Even if you do not
have the background in science to be familiar with all of the concepts
presented here, the ending packs more impact than any other book that I've ever
read. Don't read the end of the story first!

This is by far my favorite
story of all those I have written.

After
all, I undertook to tell several trillion years of human history in the space
of a short story and I leave it to you as to how well I succeeded. I also
undertook another task, but I won't tell you what that was lest l spoil the
story for you.

It
is a curious fact that innumerable readers have asked me if I wrote this story.
They seem never to remember the title of the story or (for sure) the author,
except for the vague thought it might be me. But, of course, they never forget
the story itself especially the ending. The idea seems to drown out everything
-- and I'm satisfied that it should.

The
last question was asked for the first time, half in jest, on May 21, 2061, at a
time when humanity first stepped into the light. The question came about as a
result of a five-dollar bet over highballs, and it happened this way:

Alexander
Adell and Bertram Lupov
were two of the faithful attendants of Multivac. As
well as any human beings could, they knew what lay behind the cold, clicking,
flashing face -- miles and miles of face -- of that giant computer. They had at
least a vague notion of the general plan of relays and circuits that had long
since grown past the point where any single human could possibly have a firm
grasp of the whole.

Multivac was self-adjusting and self-correcting. It had to
be, for nothing human could adjust and correct it quickly enough or even
adequately enough. So Adell and Lupov
attended the monstrous giant only lightly and superficially, yet as well as any
men could. They fed it data, adjusted questions to its needs and translated the
answers that were issued. Certainly they, and all others like them, were fully
entitled to share in the glory that was Multivac's.

For
decades, Multivac had helped design the ships and
plot the trajectories that enabled man to reach the Moon, Mars, and Venus, but
past that, Earth's poor resources could not support the ships. Too much energy
was needed for the long trips. Earth exploited its coal and uranium with
increasing efficiency, but there was only so much of
both.

But
slowly Multivac learned enough to answer deeper
questions more fundamentally, and on May 14, 2061, what had been theory, became
fact.

The
energy of the sun was stored, converted, and utilized directly on a planet-wide
scale. All Earth turned off its burning coal, its fissioning
uranium, and flipped the switch that connected all of it to a small station,
one mile in diameter, circling the Earth at half the distance of the Moon. All
Earth ran by invisible beams of sunpower.

Seven
days had not sufficed to dim the glory of it and Adell
and Lupov finally managed to escape from the public
functions, and to meet in quiet where no one would think of looking for them,
in the deserted underground chambers, where portions of the mighty buried body
of Multivac showed. Unattended, idling, sorting data
with contented lazy clickings, Multivac,
too, had earned its vacation and the boys appreciated that. They had no
intention, originally, of disturbing it.

They
had brought a bottle with them, and their only concern at the moment was to
relax in the company of each other and the bottle.

"It's
amazing when you think of it," said Adell. His
broad face had lines of weariness in it, and he stirred his drink slowly with a
glass rod, watching the cubes of ice slur clumsily about. "All the energy
we can possibly ever use for free. Enough energy, if we wanted to draw on it,
to melt all Earth into a big drop of impure liquid iron, and still never miss
the energy so used. All the energy we could ever use, forever and forever and
forever."

Lupov cocked his head sideways. He had a trick of doing
that when he wanted to be contrary, and he wanted to be contrary now, partly
because he had had to carry the ice and glassware. "Not forever," he
said.

"Oh,
hell, just about forever. Till the sun runs down, Bert."

"That's
not forever."

"All
right, then. Billions and billions of years.Ten billion, maybe. Are you satisfied?"

Lupov put his fingers through his thinning hair as though
to reassure himself that some was still left and sipped gently at his own
drink. "Ten billion years isn't forever."

"Well,
it will last our time, won't it?"

"So
would the coal and uranium."

"All
right, but now we can hook up each individual spaceship to the Solar Station,
and it can go to Pluto and back a million times without ever worrying about
fuel. You can't do that on coal and uranium. Ask Multivac,
if you don't believe me.

"I
don't have to ask Multivac. I know that."

"Then
stop running down what Multivac's done for us,"
said Adell, blazing up, "It did all right."

"Who
says it didn't? What I say is that a sun won't last forever. That's all I'm
saying. We're safe for ten billion years, but then what?" Lupow pointed a slightly shaky finger at the other.
"And don't say we'll switch to another sun."

There
was silence for a while. Adell put his glass to his
lips only occasionally, and Lupov's eyes slowly
closed. They rested.

"Sure
you are. You're weak on logic, that's the trouble with you. You're like the guy
in the story who was caught in a sudden shower and who ran to a grove of trees
and got under one. He wasn't worried, you see, because he figured when one tree
got wet through, he would just get under another one."

"I
get it," said Adell. "Don't shout. When the
sun is done, the other stars will be gone, too."

"Darn
right they will," muttered Lupov. "It all
had a beginning in the original cosmic explosion, whatever that was, and it'll
all have an end when all the stars run down. Some run down faster than others.
Hell, the giants won't last a hundred million years. The sun will last ten
billion years and maybe the dwarfs will last two hundred billion for all the good
they are. But just give us a trillion years and everything will be dark.
Entropy has to increase to maximum, that's all."

"I
know all about entropy," said Adell, standing on
his dignity.

"The
hell you do."

"I
know as much as you do."

"Then
you know everything's got to run down someday."

"All right. Who says they won't?"

"You
did, you poor sap. You said we had all the energy we needed, forever. You said
'forever.'

It
was Adell's turn to be contrary. "Maybe we can
build things up again someday," he said.

"Never."

"Why not?Someday."

"Never."

"Ask
Multivac."

"You
ask Multivac. I dare you. Five dollars says it can't
be done."

Adell was just drunk enough to try, just sober enough to be
able to phrase the necessary symbols and operations into a question which, in
words, might have corresponded to this: Will mankind one day without the net
expenditure of energy be able to restore the sun to its full youthfulness even
after it had died of old age?

Or
maybe it could be put more simply like this: How can the net amount of entropy
of the universe be massively decreased?

Then,
just as the frightened technicians felt they could hold their breath no longer,
there was a sudden springing to life of the teletype attached to that portion
of Multivac. Five words were printed: INSUFFICIENT
DATA FOR MEANINGFUL ANSWER.

"No
bet," whispered Lupov. They left hurriedly.

By
next morning, the two, plagued with throbbing head and cottony mouth, had
forgotten the incident.

Jerrodd, Jerrodine, and Jerrodette I and II watched the starry picture in the visiplate change as the passage through hyperspace was
completed in its non-time lapse. At once, the even powdering of stars gave way
to the predominance of a single bright shining disk, the size of a marble,
centered on the viewing-screen.

"That's
X-23," said Jerrodd confidently. His thin hands
clamped tightly behind his back and the knuckles whitened.

The
little Jerrodettes, both girls, had experienced the
hyperspace passage for the first time in their lives and were self-conscious
over the momentary sensation of insideoutness. They
buried their giggles and chased one another wildly about their mother,
screaming, "We've reached X-23 -- we've reached X-23 -- we've --"

"Quiet,
children." said Jerrodine sharply. "Are you
sure, Jerrodd?"

"What
is there to be but sure?" asked Jerrodd,
glancing up at the bulge of featureless metal just under the ceiling. It ran
the length of the room, disappearing through the wall at either end. It was as
long as the ship.

Jerrodd scarcely knew a thing about the thick rod of metal
except that it was called a Microvac, that one asked
it questions if one wished; that if one did not it still had its task of
guiding the ship to a preordered destination; of feeding on energies from the
various Sub-galactic Power Stations; of computing the equations for the hyperspatial jumps.

Jerrodd and his family had only to wait and live in the
comfortable residence quarters of the ship. Someone had once told Jerrodd that the "ac" at the end of "Microvac" stood for ''automatic computer" in
ancient English, but he was on the edge of forgetting even that.

Jerrodine's eyes were moist as she watched the visiplate. "I can't help it. I feel funny about
leaving Earth."

"Why,
for Pete's sake?" demanded Jerrodd. "We had
nothing there. We'll have everything on X-23. You won't be alone. You won't be
a pioneer. There are over a million people on the planet already. Good Lord,
our great-grandchildren will be looking for new worlds because X-23 will be
overcrowded." Then, after a reflective pause, "I tell you, it's a
lucky thing the computers worked out interstellar travel the way the race is
growing."

"I
know, I know," said Jerrodine miserably.

Jerrodette I said promptly, "Our Microvac
is the best Microvac in the world."

"I
think so, too," said Jerrodd, tousling her hair.

It
was a nice feeling to have a Microvac of your own and
Jerrodd was glad he was part of his generation and no
other. In his father's youth, the only computers had been tremendous machines
taking up a hundred square miles of land. There was only one to a planet.
Planetary ACs they were called. They had been growing
in size steadily for a thousand years and then, all at once, came refinement.
In place of transistors, had come molecular valves so that even the largest
Planetary AC could be put into a space only half the volume of a spaceship.

Jerrodd felt uplifted, as he always did when he thought
that his own personal Microvac was many times more
complicated than the ancient and primitive Multivac
that had first tamed the Sun, and almost as complicated as Earth's Planetarv AC (the largest) that had first solved the
problem of hyperspatial travel and had made trips to
the stars possible.

"So
many stars, so many planets," sighedJerrodine, busy with her own thoughts. "I suppose
families will be going out to new planets forever, the way we are now."

"Not
forever," said Jerrodd, with a smile. "It
will all stop someday, but not for billions of years. Many
billions. Even the stars run down, you know. Entropy must increase.

"What's
entropy, daddy?" shrilled Jerrodette II.

"Entropy,
little sweet, is just a word which means the amount of running-down of the
universe. Everything runs down, you know, like your little walkie-talkie robot,
remember?"

"Can't
you just put in a new power-unit, like with my robot?"

"The
stars are the power-units. dear. Once they're gone,
there are no more power-units."

Jerrodette I at once set up a howl. "Don't let them,
daddy. Don't let the stars run down."

"Now
look what you've done," whispered Jerrodine,
exasperated.

"How
was I to know it would frighten them?" Jerrodd
whispered back,

"Ask
the Microvac," wailed JerrodetteI.
"Ask him how to turn the stars on again."

"Go
ahead," said Jerrodine. "It will quiet them
down." (Jerrodette II was beginning to cry,
also.)

Jerrodd cupped the strip or thin cellufilm
and said cheerfully, "See now, the Microvac says
it will take care of everything when the time comes so don't worry."

Jerrodine said, "And now, children, it's time for bed.
We'll be in our new home soon."

Jerrodd read the words on the cellufilm
again before destroying it: INSUFICIENT DATA FOR MEANINGFUL ANSWER.

He
shrugged and looked at the visiplate. X-23 was just
ahead.

VJ-23X
of Lameth stared into the black depths of the three-dimensional,
small-scale map of the Galaxy and said, "Are we ridiculous, I wonder in
being so concerned about the matter?"

MQ-17J
of Nicron shook his head. "I think not. You know
the Galaxy will be filled in five years at the present rate of expansion."

Both
seemed in their early twenties, both were tall and perfectly formed.

"Still,"
said VJ-23X, "I hesitate to submit a pessimistic report to the Galactic
Council."

"I
wouldn't consider any other kind of report. Stir them up a bit. We've got to
stir them up."

VJ-23X
sighed. "Space is infinite. A hundred billion Galaxies are there for the
taking. More."

"A
hundred billion is not infinite and it's getting less infinite all the time.
Consider! Twenty thousand years ago, mankind first solved the problem of
utilizing stellar energy, and a few centuries later, interstellar travel became
possible. It took mankind a million years to fill one small world and then only
fifteen thousand years to fill the rest of the Galaxy. Now the population
doubles every ten years --

VJ-23X
interrupted. "We can thank immortality for that."

"Very well. Immortality exists and we have to take it
into account. I admit it has its seamy side, this immortality. The Galactic AC
has solved many problems for us, but in solving the problem of preventing old
age and death, it has undone all its other solutions."

"Yet
you wouldn't want to abandon life, I suppose."

"Not at all," snapped MQ-17J, softening it at once to,
"Not yet. I'm by no means old enough. How old are you?"

"Two hundred twenty-three. And you?"

"I'm
still under two hundred. --But to get back to my point. Population doubles
every ten years. Once this GaIaxy is filled, we'll
have filled another in ten years. Another ten years and we'll have filled two
more. Another decade, four more. In a hundred years,
we'll have filled a thousand Galaxies. In a thousand years, a million Galaxies.
In ten thousand years, the entire known universe.Then what?"

VJ-23X
said, "As a side issue, there's a problem of transportation. I wonder how
many sunpower units it will take to move Galaxies of
individuals from one Galaxy to the next."

"A very good point. Already, mankind consumes two sunpower units per year."

"Most
of it's wasted. After all, our own Galaxy alone pours out a thousand sunpower units a year and we only use two of those."

"Granted,
but even with a hundred per cent efficiency, we only stave off the end. Our
energy requirements are going up in a geometric progression even faster than
our population. We'll run out of energy even sooner than we run out of
Galaxies. A good point.A very good
point."

"We'll
just have to build new stars out of interstellar gas."

"Or
out of dissipated heat?" asked MQ-17J, sarcastically.

"There
may be some way to reverse entropy. We ought to ask the Galactic AC."

VJ-23X
was not really serious, but MQ-17J pulled out his AC-contact from his pocket
and placed it on the table before him.

"I've
half a mind to," he said. "It's something the human race will have to
face someday."

He
stared somberly at his small AC-contact. It was only two inches cubed and
nothing in itself, but it was connected through hyperspace with the great
Galactic AC that served all mankind. Hyperspace considered,
it was an integral part of the Galactic AC.

MQ-17J
paused to wonder if someday in his immortal life he would get to see the
Galactic AC. It was on a little world of its own, a spider webbing of
force-beams holding the matter within which surges of submesons
took the place of the old clumsy molecular valves. Yet despite its sub-etheric workings, the Galactic AC was known to be a full
thousand feet across.

VJ-23X
looked startled and said at once, "Oh, say, I didn't really mean to have
you ask that."

"Why not?"

"We
both know entropy can't be reversed. You can't turn smoke and ash back into a
tree."

"Do
you have trees on your world?" asked MQ-17J.

The
sound of the Galactic AC startled them into silence. Its voice came thin and
beautiful out of the small AC-contact on the desk. It said: THERE IS
INSUFFICIENT DATA FOR A MEANINGFUL ANSWER.

VJ-23X
said, "See!"

The
two men thereupon returned to the question of the report they were to make to
the Galactic Council.

Zee
Prime's mind spanned the new Galaxy with a faint interest in the countless
twists of stars that powdered it. He had never seen this one before. Would he
ever see them all? So many of them, each with its load of
humanity. --But a load that was almost a dead weight. More and more, the
real essence of men was to be found out here, in space.

Minds,
not bodies! The immortal bodies remained back on the planets, in suspension
over the eons. Sometimes they roused for material activity but that was growing
rarer. Few new individuals were coming into existence to join the incredibly
mighty throng, but what matter? There was little room in the Universe for new
individuals.

Zee
Prime was roused out of his reverie upon coming across the wispy tendrils of
another mind.

"I
am Zee Prime," said Zee Prime. "And you?"

"I
am Dee Sub Wun. Your
Galaxy?"

"We
call it only the Galaxy. And you?"

"We
call ours the same. All men call their Galaxy their Galaxy and nothing more. Why not?"

"True.
Since all Galaxies are the same."

"Not
all Galaxies. On one particular Galaxy the race of man must have originated.
That makes it different."

Zee
Prime said, "On which one?"

"I
cannot say. The Universal AC would know."

"Shall
we ask him? I am suddenly curious."

Zee
Prime's perceptions broadened until the Galaxies themselves shrank and became a
new, more diffuse powdering on a much larger background. So many hundreds of
billions of them, all with their immortal beings, all carrying their load of
intelligences with minds that drifted freely through space. And yet one of them
was unique among them all in being the original Galaxy. One of them had, in its
vague and distant past, a period when it was the only Galaxy populated by man.

Zee
Prime was consumed with curiosity to see this Galaxy and he called out:
"Universal AC! On which Galaxy did mankind originate?"

The
Universal AC heard, for on every world and throughout space, it had its
receptors ready, and each receptor led through hyperspace to some unknown point
where the Universal AC kept itself aloof.

Zee
Prime knew of only one man whose thoughts had penetrated within sensing
distance of Universal AC, and he reported only a shining globe, two feet
across, difficult to see.

"But
how can that be all of Universal AC?" Zee Prime had asked.

"Most
of it," had been the answer, "is in hyperspace.
In what form it is there I cannot imagine."

Nor
could anyone, for the day had long since passed, Zee Prime knew, when any man
had any part of the making of a Universal AC. Each Universal AC designed and
constructed its successor. Each, during its existence of a million years or
more accumulated the necessary data to build a better and more intricate, more
capable successor in which its own store of data and individuality would be
submerged.

The
Universal AC interrupted Zee Prime's wandering thoughts, not with words, but
with guidance. Zee Prime's mentality was guided into the dim sea of Galaxies
and one in particular enlarged into stars.

A
thought came, infinitely distant, but infinitely clear. "THIS IS THE
ORIGINAL GALAXY OF MAN."

But
it was the same after all, the same as any other, and Lee Prime stifled his
disappointment.

Dee
Sub Wun, whose mind had accompanied the other, said
suddenly, "And is one of these stars the original star of Man?"

The
Universal AC said, "MAN'S ORIGINAL STAR HAS GONE NOVA. IT IS A WHITE
DWARF"

"Did
the men upon it die?" asked Lee Prime, startled and without thinking.

The
Universal AC said, "A NEW WORLD, AS IN SUCH CASES WAS CONSTRUCTED FOR
THEIR PHYSICAL BODIES IN TlME."

"Yes,
of course," said Zee Prime, but a sense of loss overwhelmed him even so.
His mind released its hold on the original Galaxy of Man, let it spring back
and lose itself among the blurred pin points. He never wanted to see it again.

Dee
Sub Wun said, "What is wrong?"

"The
stars are dying. The original star is dead."

"They
must all die. Why not?"

"But
when all energy is gone, our bodies will finally die, and you and I with
them."

"It
will take billions of years."

"I
do not wish it to happen even after billions of years. Universal AC! How may
stars be kept from dying?"

Dee
Sub Wun said in amusement, "You're asking how
entropy might be reversed in direction."

And
the Universal AC answered: "THERE IS AS YET INSUFFICIENT DATA FOR A
MEANINGFUL ANSWER."

Zee
Prime's thoughts fled back to his own Galaxy. He gave no further thought to Dee
Sub Wun, whose body might be waiting on a Galaxy a
trillion light-years away, or on the star next to Zee Prime's own. It didn't matter.

Unhappily,
Zee Prime began collecting interstellar hydrogen out of which to build a small
star of his own. If the stars must someday die, at least some could yet be
built.

Man
considered with himself, for in a way, Man, mentally, was one. He consisted of
a trillion, trillion, trillion ageless bodies, each in its place, each resting
quiet and incorruptible, each cared for by perfect automatons, equally
incorruptible, while the minds of all the bodies freely melted one into the
other, indistinguishable.

Man
said, "The Universe is dying."

Man
looked about at the dimming Galaxies. The giant stars, spendthrifts, were gone
long ago, back in the dimmest of the dim far past. Almost all stars were white
dwarfs, fading to the end.

New
stars had been built of the dust between the stars, some by natural processes,
some by Man himself, and those were going, too. White dwarfs might yet be
crashed together and of the mighty forces so released, new stars built, but
only one star for every thousand white dwarfs destroyed, and those would come
to an end, too.

Man
said, "Carefully husbanded, as directed by the Cosmic AC, the energy that
is even yet left in all the Universe will last for billions of years."

"But
even so," said Man, "eventually it will all come to an end. However
it may be husbanded, however stretched out, the energy once expended is gone
and cannot be restored. Entropy must increase forever to the maximum."

Man
said, "Can entropy not be reversed? Let us ask the Cosmic AC."

The
Cosmic AC surrounded them but not in space. Not a fragment of it was in space.
It was in hyperspace and made of something that was neither matter nor energy.
The question of its size and nature no longer had meaning in any terms that Man
could comprehend.

"Cosmic
AC," said Man, "how may entropy be reversed?"

The
Cosmic AC said, "THERE IS AS YET INSUFFICIENT DATA FOR A MEANINGFUL
ANSWER."

Man
said, "Collect additional data."

The
Cosmic AC said, 'I WILL DO S0. I HAVE BEEN DOING SO FOR A HUNDRED BILLION
YEARS. MY PREDECESORS AND I HAVE BEEN ASKED THIS QUESTION MANY TlMES. ALL THE DATA I HAVE REMAINS INSUFFICIENT.

"Will
there come a time," said Man, 'when data will be sufficient or is the
problem insoluble in all conceivable circumstances?"

The
Cosmic AC said, "NO PROBLEM IS INSOLUBLE IN ALL CONCEIVABLE
CIRCUMSTANCES."

Man
said, "When will you have enough data to answer the question?"

The
Cosmic AC said, "THERE IS AS YET INSUFFICIENT DATA FOR A MEANINGFUL
ANSWER."

"Will
you keep working on it?" asked Man.

The
Cosmic AC said, "I WILL."

Man
said, "We shall wait."

The
stars and Galaxies died and snuffed out, and space grew black after ten
trillion years of running down.

One
by one Man fused with AC, each physical body losing its mental identity in a
manner that was somehow not a loss but a gain.

Man's
last mind paused before fusion, looking over a space that included nothing but
the dregs of one last dark star and nothing besides but incredibly thin matter,
agitated randomly by the tag ends of heat wearing out, asymptotically, to the
absolute zero.

Man
said, "AC, is this the end? Can this chaos not be reversed into the
Universe once more? Can that not be done?"

AC
said, "THERE IS AS YET INSUFFICIENT DATA FOR A MEANINGFUL ANSWER."

Man's
last mind fused and only AC existed -- and that in hyperspace.

Matter
and energy had ended and with it space and time. Even AC existed only for the
sake of the one last question that it had never answered from the time a
half-drunken computer [technician] ten trillion years before had asked the
question of a computer that was to AC far less than was a man to Man.

All
other questions had been answered, and until this last question was answered
also, AC might not release his consciousness.

All
collected data had come to a final end. Nothing was left to be collected.

But
all collected data had yet to be completely correlated and put together in all
possible relationships.

A
timeless interval was spent in doing that.

And
it came to pass that AC learned how to reverse the direction of entropy.

But
there was now no man to whom AC might give the answer of the last question. No
matter. The answer -- by demonstration -- would take care of that, too.

For
another timeless interval, AC thought how best to do this. Carefully, AC
organized the program.

The
consciousness of AC encompassed all of what had once been a Universe and
brooded over what was now Chaos. Step by step, it must be done.